氧化物修饰和氮掺杂生物基碳材料的制备及其在锂硫电池中的应用

发布时间：2018-07-06 21:24

本文选题：AZO@C + 木棉纤维　；参考：《浙江工业大学》2017年硕士论文

【摘要】：锂硫电池因为具有比容量高、能量密度大、资源丰富和成本低廉等优点,而受到了研究者们的广泛关注。但是,硫正极也面临着许多问题,比如硫的导电性较差,“穿梭效应”,多硫化锂的沉积不可控,硫的体积效应较为严重等。这些问题导致了锂硫电池在实际使用中容量衰减明显,库伦效率低下。为了解决这些问题,本文从材料的微观结构入手,结合表面修饰和元素掺杂等手段,分别以木棉纤维和鸡蛋清为碳源和模板,合成了铝掺杂氧化锌/碳复合材料(AZO@C)和掺氮生物多孔碳两种改性碳材料,并对其进行了相组成、形貌和微观结构表征,以及电化学性能测试。主要研究结果如下:(1)在第三章中,以木棉纤维为模板和碳源,合成了AZO@C复合材料,并用XRD、XPS、SEM和TEM等手段对其进行了结构和形貌表征。结果显示,煅烧研磨后的木棉基底为微米片状结构,其表面上修饰有15nm到30nm的AZO纳米颗粒,并且具有良好的结晶性。(2)在第四章中,将AZO@C等复合材料与单质硫混合制备了硫正极。电化学测试结果表明,AZO@C/S电极展现出了优于Zn O@C/S和Al2O3@C/S电极的电化学性能。当电流密度为0.1C时,AZO@C/S电极在100次循环之后依然保持着927 m Ah g-1的可逆(3)容量;当电流密度增至0.5C时,300次循环后其放电容量依然可以保持在544 m Ah g-1,换算成每圈循环的容量损失率为0.039%。即使在硫载量达到6.69 mg cm-2时,电池在0.5C循环100次后仍有466 m Ah g-1的容量。如此优异的电化学性能主要归因于极性的AZO颗粒具有较高的导电性,它能有效地抑制“穿梭效应”并为多硫化锂的转变提供反应动力。(4)在第五章中,以鸡蛋清同时作为碳源和氮源,制备了氮掺杂的多孔碳材料。SEM、BET等结果表明该碳材料具有良好的多孔结构。与硫复合制成硫电极后,复合材料展现出了良好的电化学性能:以硫脲为外加氮源制备的N-C/S电极在0.1C电流密度下循环200次后依然有近700 m Ah g-1的可逆容量,容量保持率为84%,远超过普通的活性炭材料。电池性能的提升主要是因为氮的掺杂使得碳材料中产生了带正电的活性位点,这些位点能够有效地吸附带负电的多硫根离子,从而减缓了多硫化锂在电解液中的溶解。
[Abstract]:Lithium-sulfur batteries have attracted much attention due to their high specific capacity, high energy density, rich resources and low cost. However, sulfur cathode also faces many problems, such as poor conductivity of sulfur, "shuttle effect", uncontrollable deposition of lithium polysulfide, and serious volume effect of sulfur. These problems lead to obvious capacity attenuation and low Coulomb efficiency in practical use of lithium-sulfur batteries. In order to solve these problems, this paper starts with the microstructure of the material, combines the surface modification and element doping, respectively, using kapok fiber and egg white as carbon source and template. Aluminum-doped zinc oxide / carbon composites (AZOOC) and nitrogen-doped biological porous carbon composites were synthesized, and their phase composition, morphology, microstructure and electrochemical properties were characterized. The main results are as follows: (1) in chapter 3, AZOOC composites were synthesized using kapok fiber as template and carbon source. The structure and morphology of AZOOC composites were characterized by means of XRDX, XPS, SEM and TEM. The results show that the calcined kapok substrate is micrometer lamellar structure, the surface of which is modified with 15nm to 30nm nanoparticles, and has good crystallinity. (2) in the fourth chapter, the composite materials such as AZOOC and simple sulfur are mixed to prepare the sulfur positive electrode. The electrochemical test results show that the AZO @ C / S electrode exhibits better electrochemical performance than the Zn-Or C / S and Al _ 2O _ 3 @ C / S electrodes. When the current density is 0.1 C, the reversible (3) capacity of the AZO @ C / S electrode remains at 927 mAh g-1 after 100 cycles. When the current density is increased to 0.5 C, the discharge capacity of 300 cycles can be maintained at 544 mAh g-1, and the loss rate of capacity converted to each cycle is 0.039%. Even when the sulfur load reached 6.69 mg cm-2, the battery still had the capacity of 466mAh g-1 after 100th cycle at 0.5C. Such excellent electrochemical properties are mainly attributed to the high conductivity of polar AZO particles, which can effectively suppress the "shuttle effect" and provide the reaction power for the transition of lithium polysulfide. (4) in Chapter 5, Using egg white as carbon source and nitrogen source, N-doped porous carbon material, SEMM-BET, was prepared. The results showed that the carbon material had a good porous structure. After recombination with sulfur, the composite showed good electrochemical performance: the N-C / S electrode with thiourea as the external nitrogen source still had a reversible capacity of nearly 700 mAh g-1 after 200 cycles at 0.1C current density. Capacity retention is 84%, far more than ordinary activated carbon materials. The improvement of battery performance is mainly due to the presence of positively charged active sites in carbon due to nitrogen doping, which can effectively adsorb negatively charged polysulfide ions, thus slowing down the dissolution of lithium polysulfide in electrolyte.
【学位授予单位】：浙江工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ127.11;TB33;TM912

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